title: The activation of P2X7 receptor induces cathepsin D-dependent production of a 20-kDa form of IL-1β under acidic extracellular pH in LPS-primed microglial cells.
abstract: The potent pro-inflammatory cytokine, interleukin-1β (IL-1β), is synthesized as an inactive 33-kDa precursor (pro-IL-1β) and is processed by caspase 1 into the bioactive 17-kDa mature form. The P2X7 receptor, an ATP-gated cation channel, plays an essential role in caspase 1 activation, production and release of mature bioactive 17-kDa form. We recently reported ATP induces the release of an unconventional 20-kDa form of IL-1β (p20-IL-1β) from lipopolysaccharide-primed microglial cells. Emerging evidence suggests physiological relevance for p20-IL-1β; however, the underlying mechanisms for its production and release remain unknown. Here, we investigated the pathways involved in the ATP-induced production of p20-IL-1β using lipopolysaccharide-primed mouse microglial cells. The activation of P2X7 receptor by ATP triggered p20-IL-1β production under acidic extracellular conditions. ATP-induced p20-IL-1β production was blocked by pepstatin A, a potent inhibitor of the lysosomal protease, cathepsin D. The removal of extracellular Ca(2+) inhibited the p20-IL-1β production as well as ATP-induced cathepsin D release via lysosome exocytosis. The acidic extracellular pH also facilitated the dilatation of membrane pore after ATP stimulation. Since facilitation of pore dilatation results in cytolysis accompanied with cytoplasmic pro-IL-1β leakage, our data suggest the leaked pro-IL-1β is processed into p20-IL-1β by cathepsin D released after ATP stimulation under acidic extracellular conditions.
authors.affiliation: Transgenic Animal Research Center, National Institute of Agrobiological Sciences, Ohwashi, Tsukuba, Ibaraki, Japan.
authors.forename: Takato
authors.initials: T
authors.lastname: Takenouchi
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Iwamaru
authors.forename: Shuei
authors.initials: S
authors.lastname: Sugama
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Tsukimoto
authors.forename: Masayo
authors.initials: M
authors.lastname: Fujita
authors.forename: Akio
authors.initials: A
authors.lastname: Sekigawa
authors.forename: Kazunari
authors.initials: K
authors.lastname: Sekiyama
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Sato
authors.forename: Shuji
authors.initials: S
authors.lastname: Kojima
authors.forename: Bruno
authors.initials: B
authors.lastname: Conti
authors.forename: Makoto
authors.initials: M
authors.lastname: Hashimoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kitani
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D020170:Caspase 1 / Q000378:metabolism; D002402:Cathepsin D / Q000494:pharmacology*; D002460:Cell Line; D005089:Exocytosis / Q000187:drug effects; D005110:Extracellular Space / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D053583:Interleukin-1beta / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D010436:Pepstatins / Q000494:pharmacology; D058486:Receptors, Purinergic P2X7 / Q000187:drug effects*
chemical_list: D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D009419:Nerve Tissue Proteins; D010436:Pepstatins; D058486:Receptors, Purinergic P2X7; D000255:Adenosine Triphosphate; D020170:Caspase 1; D002402:Cathepsin D; C031375:pepstatin